This invention relates to a method of producing foam-filled stud walls.
It has long been known that a foam-filled wood stud wall is very desirable from an insulation (i.e. heat transfer) viewpoint, and various methods have been used in the past to produce such walls.
No suitable method has yet been developed to facilitate rapid and efficient prefabrication of such walls on an assembly-line basis. The present invention is directed toward providing a suitable assembly line method for implementing the method for producing prefabricated foam-filled walls.
The type of wall intended to be filled is the type commonly used in wood frame construction, i.e. a wall having a base plate, a top plate, window and door openings, and a number of spaced vertical studs, the plates and studs most commonly being either nominal two-by-four or two-by-six lumber. However, this invention is not limited either to specific stud sizes or spacings, nor to any specific stud material.
In the prior art, urethane insulation has been applied on site to standing stud walls, typically by spraying a spray-type foam onto the wall and building up an insulating layer roughly an inch at a time. As spray-type foams are highly exothermic, the layers of insulation must be built up gradually. This type of system is generally cumbersome, messy and may product an uneven surface with no certainty that all voids, including corner cavities are filled.
Another attempted solution in the prior art has been to inject measured amounts of foam between panels, but this is difficult or impossible to do in the case of prefabricated stud walls, especially when dealing with varying wall sizes. Injecting an incorrect amount of foam may result either in voids in the insulation, or in the wall being forced apart by the expanding foam. The latter problems may possibly be avoided by utilizing a full press on both sides of the wall, but in addition to requiring more elaborate equipment, this also means that non-standard wall sizes cannot be readily accommodated, nor can window openings and the like.
In the prior art, various types of equipment have been used for injecting foam into double-membrane panels such as those found in metal garage doors, for example. Such systems suffer from a number of serious drawbacks which prevent or severely restrict their applicability to stud walls. These drawbacks include the fact that a complete filling may not take place, and may not even be possible, if the panel includes window and door openings. Another serious problem with this type of system is that, since both front and rear panels must be in place to contain the foam, either a finished interior surface, or a superfluous interior panel (to be covered later by a finished surface) must be provided. If a finished interior surface such as gypsum board or "drywall" is installed at the plant location, further handling of the panel is made far more difficult. This type of panel would not only weigh more, but would need to be handled with great care in order to avoid damaging the finished surface.
A method for producing a prefabricated insulated wall panel is disclosed in U.S. Pat. No. 4,409,768 granted to Boden in October 1983. The preferred embodiment of this invention employs multiple dams to contain the foam introduced into a wall. A single dam is used to cover the area to be filled. A stud wall is placed into a backplate and then a series of plates is placed upon the stud wall. Although a satisfactory wall may be produced, Boden is not particularly well suited for production line methods of manufacturing. The use of a single dam covering a full stud wall as the foam sets is highly inefficient and not cost effective.
A method for insulating walls is disclosed in U.S. Pat. No. 4,093,411, granted to Lee in June 1978. Lee teaches a process for covering a surface with foam using a machine which travels along the surface. The wall produced will have effective heat transfer properties but may not be satisfactory. If the studs are warped or vary in width, the wall will not be uniform nor will a planar surface be achieved. Further, the foam material will exude from the stud cavity which will require removal.
Lee discloses an apparatus having a continuous or endless belt, and does not suggest the use of a single plate moved along the stud wall in discrete steps with a delay between such steps to allow for setting of the foam. It should be noted that although Lee shows a pressure plate behind the belt, it merely serves to limit the expansion of the foam, and has no means for urging the belt into contact with underlying studs so as to straighten any misalignment or to adjust for varying thickness.
Applicant has found that after the foam has been injected into the stud wall and allowed to cure, the foam will continue to expand for about 24 hours by about 1%-2% of its initially cured volume. This phenomenon is known as "slow grow". The foam will bulge outwardly from the stud cavity preventing a sheet of drywall to be applied directly thereto. Either the foam must be continuously restrained to prevent the foam from expanding or the excess foam must be removed mechanically. In either case, the efficiency of manufacturing is greatly diminished.
In the former case, a double-framed membrane can be used to restrict the expansion of the foam, which adds material costs to the finished product. If the inner surface is to be left open, the stud wall must be kept in a press for up to 24 hours while the foam fully cures, which greatly restricts the production speed of a finished wall product.
In the latter case, a considerable labour cost is added to the finished product to remove the excess foam to present a planar surface. Further, sanding of the foam releases foam particles and dust into the air which requires special health and safety precautions to be exercised.
It is highly desirable to have a method which permits the filling not only of uniform size wall sections without window openings or the like, but also the filling of varying sizes of wall sections with varying sizes and locations of window openings. It is also highly desirable to have a method which permits the filling of walls without requiring the presence of any interior panel, finished or otherwise.
It is also desirable to have a method which presents a finished surface substantially planar with the studs, while removing a minimum of excess foam.